Yes, I was also referring to a scenario where you create a single-person company and have a single source of revenue from a de-facto employer.
Is it really illegal in France or do you just owe more taxes/contributions than if you had multiple clients (which would allow you to take part of the revenue as company profits, instead of having to channel it all as a salary)?
Looking at your comment [0] it sounds like it might not be illegal (provided you pay the required taxes/contributions)?